Highly pathogenic avian influenza A subtype H5N8
Highly pathogenic avian influenza (HPAI) H5N8 outbreaks in poultry farms have been reported in Asia and Europe since January and November 2014, respectively. The entry of HPAI H5N8 into Europe and its subsequent spread within Europe are two separate events with possibly different transmission vectors. Following epidemiological investigations of infected poultry holdings, there is not yet a clear indication of the source of the virus. There are no known direct bird migration routes from Asia to western Europe. It has been hypothesised that long-distance transmission of HPAI viruses could occur as a result of cross-infection between different birds in north Eurasian breeding areas, but this hypothesis needs further investigation. HPAI H5N8 has been detected in wild bird populations in Germany and the Netherlands. Direct contact between wild birds and farmed birds in the affected holdings was unlikely. It is more plausible that indirect introduction of HPAI H5N8 to poultry holdings via humans, vehicles, equipment, fomites, live animals and/or animal-derived products contaminated with virus (for instance in faeces) of infected birds took place. Investigations in the Netherlands suggest separate introductions into four holdings and one between-farm transmission. Assessing biosecurity procedures is recommended with a focus on segregation, cleaning and disinfection, and improving where necessary. Given the apparent low pathogenicity of HPAI H5N8 for several wild bird species, focused strategic and proportionate enhancement of active and passive surveillance of living and dead wild birds in the high risk areas would improve the understanding of the risk of virus transmission to poultry. It might also facilitate the design of targeted measures to reduce the risk of virus transmission between poultry and wild birds. Timely updated analyses on the evolving situation within the European Union are required, as well as assessment of all transmission routes that might transport HPAI viruses from Asia to Europe.